Only refers to it as a synonym for "Megalopolis" - Generally the term describes any densely populated social and economic entity encompassing two or more cities and the increasingly urbanized space between them. It particularly came to describe the urbanized region of the northeastern U.S. that arose in the second half of the 20th century. Stretching between the metropolitan areas of Boston on the northeast to Washington, D.C., on the southwest, it included the metropolitan areas of New York City, Philadelphia, and Baltimore, Md. The name, meaning “great city,” was coined by French geographer Jean Gottmann. (Merriam-Webster Dictionary) http://www.merriam-webster.com/dictionary/megacity
A very large city, typically one with a population of over ten million people. (Oxford English Dictionary)
http://www.oxforddictionaries.com/us/definition/american_english/megacity
Only refers to it as a synonym for "Megalopolis" -
Generally the term describes any densely populated social and economic entity encompassing two or more cities and the increasingly urbanized space between them. It particularly came to describe the urbanized region of the northeastern U.S. that arose in the second half of the 20th century. Stretching between the metropolitan areas of Boston on the northeast to Washington, D.C., on the southwest, it included the metropolitan areas of New York City, Philadelphia, and Baltimore, Md. The name, meaning “great city,” was coined by French geographer Jean Gottmann. (Merriam-Webster Dictionary)
http://www.merriam-webster.com/dictionary/megacity
The Megacities Project: http://www.mega-cities.net/
The World's Fastest Growing Megacities, Forbes, April 2013:
http://www.forbes.com/sites/joelkotkin/2013/04/08/the-worlds-fastest-growing-megacities/
National Geographic Feature on Megacities:
http://ngm.nationalgeographic.com/ngm/0211/feature3/
Rise of the Megacity: Interactive infographic, The Guardian, Oct 2012:
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=0CBEQ1Sc&url=http%3A%2F%2Fwww.theguardian.com%2Fglobal-development%2Fdatablog%2F2012%2Foct%2F04%2Frise-megacities-get-data&ei=KAEvVMGeCJH3yQT8iIKwCg&usg=AFQjCNFJaXDi60ewfqdsAl8nWQmA9nLuSw&sig2=J-ezoA3DfcpjL_JIGRmvFg&bvm=bv.76802529,d.aWw
Megacities, Global Security and the Map of the Future, Wilson Center, March 20 2012:
http://www.wilsoncenter.org/event/megacities-global-security-and-the-map-the-future
Mega Cities: The Nexus of Risk, Stimson Center,
http://www.stimson.org/topics/global-health/mega-cities-the-nexus-of-risk/
Case studies of Sao Paulo, Lagos, Karachi and Dhaka Bangladesh
Megacity Rising, ISN, October 2012:
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CDsQFjAE&url=http%3A%2F%2Fwww.isn.ethz.ch%2FDigital-Library%2FArticles%2FDetail%2F%3Fid%3D171570&ei=jwMvVOXEGNK3yASlxIGABQ&usg=AFQjCNHc1uvKlnjlfDTliX7dcHMflu6JJQ&sig2=6rWyEnRZQcAEmcM8Vdr_uw&bvm=bv.76802529,d.aWw
Megacities: Problems, Challenges and Chances: http://webs.schule.at/website/megacities/problems_en.htm
Some kind of Megacity aggegator site with links, etc. may be affiliated with UN, unclear